Dorsal-Ventral Polarity in the Drosophila Embryo

A critical step in pattern formation in Drosophila is the establishment of polarity along the two major body axes. At least 20 maternally active genes are involved in creating dorsal- ventral polarity. A variety of experiments have shown that dorsal represents the last step in the process, it acts as the ventral morphogen relating the maternal positional information to the zygotic genome. Dr. Steward has cloned and characterized the dorsal gene and found it is closely related to the vertebrate proto-oncogene c-rel. In wild type embryos, the dorsal protein is present in the cytoplasm during cleavage. After the nuclei migrate to the periphery of the embryo, a ventral to dorsal gradient of nuclear dorsal protein is established. The formation of the nuclear gradient is disrupted in mutant embryos from other maternally active dorsal-ventral polarity genes. In dorsalized mutant embryos, only cytoplasmic protein is observed, while in ventralized embryos, the nuclear gradient is shifted dorsally. Relocalization of the dorsal protein from the cytoplasm to the nucleus appears critical for dorsal to function as a morphogen. Dr. Steward proposes a number of experiments that address the question of what genes either interact with dorsal to effect the cytoplasmic versus nuclear localization or are essential for dorsal function once the protein is in the nucleus. Specifically she will perform genetic screens to isolate second site suppressors of specific dorsal mutations.